Piezoelectric crystal growing method



June 8, 1948. c. J. CHRISTENSEN 2,442,755

PIEZOELECTRIG CRYSTAL GROWING METHOD Filed June 11, 1945 2 Sheets-Sheet 1 IN VENTOR e. J. CHRISTENSEN ATTORNEY June 1948- c. J. CHRISTENSEN 2, ,7

PIEZOELECTRIC CRYSTAL GROWING METHOD Filed June 11, 1945 2 Sheets-Sheet 2 lN VE N 70/? C. J. CHRISTENSEN A TTORNE V Patented June 8, 19 i V PIEZOELECTBIO CRYSTAL GROWING METHOD Carl J. Christensen, Summit, N. 1., asslgnor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application June 11, 1945, Serial No. 598.893

17 Claims. (01. 171-327) This invention relates to piezoelectric crystals it is often desirable that the seed crystals used and particularly to seed crystals that may be utifor growing the crystal material be provided from lized for growing crystals in a nutrient solution. sources other than the manufactured material One of the objects of this invention is to reduce that is to be or could be used in the construction waste in crystalline materials. of the piezoelectric elements intended for use as Another object of this invention is to provide circuit elements in the ultimate electrical system. crystals having a relatively large usable piezo- In accordance with this invention, the diagonal electric content free from flaws. type seed plate may be cut from flawed or nor- Another object of this invention is to provide a mally Wasted crystalline ma and y t b seed crystal that may be cut from waste crystal- 1o capable of growing a good crystal bar therefrom line material and yet which may be grown to prothe grown part of the ry b being free fI'Om duce a crystal having a large proportion of crysany flawed crystal material. talline material usable for piezoelectric purposes. For a clearer understanding of the nature of This inven ion will be described particularly in this invention and the additional advantages. connection with piezoelectric crystalscomprising features and objects thereof, reference is made ammonium dihydrogen phosphate mi -1,90 to the following description taken in connection but it will be understood that it may also be emwith the accomp y drawin in wh h like bodied in many other types of crystalline ubreference characters represent like or similar stances of similar tetragonal form or otherwise. p r s nd n which:

In accordance with this invention, a seed cryso s- 1 is P p v V w Of n am n um tal plate may be cut from a crystal bar, such as y s n phesphate crystal h and a d l that of ammonium dihydrogen pho hate, 50 that seed plate in accordance with this invention; the two major faces of the seed plate are parallel P e: 2 is a perspective view of a d n Seed or nearly parallel with respect to the till plane plate as cut from the crystal b s w n Fi 1; of any one of the pyramidal cap faces of the 5 15 etside vi w of ry l b r r n from crystal bar. This type of seed plate is a useful a diagonal ed plate of the yp shown in Fig. 2; form of seed for growing a crystal bar in a nu- Figs. 4, 5 and 6 are views of a mount which trient solution. may be used for mounting and growing the seed In the construction of many types of electrical plate of Fig. 2 into a crystal bar as shown in Fissystems, piezoelectric crystal elements are often 80 5 being an e a ge V ew taken on the line .used as electrical circuit elements therein. and 5-5 of Fis- 4. and Fig. 6 e ng an enlars V w such piezoelectric elements may be cut with any of the lower left corner po f F suitable size, shape and crystallographic orienta- R rring to the drawing, Fig. 1 is a pe v tion to suit the particular application. As an Vi w o an m u dihydrogen p ph example in the case of crystalline ammonium dicrystal bar I which has been grown in a suitable hydrogen hos hate, m of t useful piezonutrient solution from a seed crystal plate 3. electric cuts are the Z-cut crystal plate, and the wn in outline y the broken lines in F s- 1- 45 degree Z-cut crystal plate, and others. Such The crystal r I. illustrated in 1. has piezoelectric elements are cut from a suitable fo r equal side or pri m feces and at the Opp crystal bar which has been grown from a seed site ends thereof there are tWO sets of foul princrystal in a suitable nutrient solution. While cipal cap or p ami l ces w i by c ve such a cry tal bar may be grown from many digtion are designated Ill planes. The optic axis ferent shapes and types of seed crystal, it is often of t crystal h r x n s alon the direction desirable, especially in connection with large scale of the B dimension f the y l b a commercial production, to grow the crystal bar the m l y perpendicular l xt 81 118 from a type of seed crystal which gives a relathe directions of the width dimensions of the tively large content of usable piezoelectric mateprism faces I. the mm p rp n i ul r rial that is free from flaws. In accordance with a-axes beins p p u r o th Op ic axis Z- thi invention, a diagonal type e plate i pm- The optic axis Z is sometimes referred to as the vided which is capable of growing a crystal bar so c-exis, and t t a y pe p c a c-axes are having a relatively larger content of usable piezo- Sometimes referred t 88 th x an Y ax s- The electric material therein than is obtained from 6-8158 Croce-section oi the crystal bar I m b other types of seed crystals of the prior art. of square shape, or of other rectangular shape In order to conserve material in connection and of any desired size. The Z-axis over-all with large scale production of crystal material, It length of the crystal bar I may be made any desired length dependent upon the length of time of its growth from the seed crystal 3 and other factors. It will be understood that the crystal bar I may be grown from a suitable seed crystal 3 in a suitable nutrient solution by any suitable crystal growing apparatus such as for example by a reciprocating rotary gyrator type crystallizer as disclosed and claimed in a copending application, Serial No. 598,691, filed June 11, 1945, by A. N. Holden, assigned to Bell Telephone Laboratories, Incorporated.

The seed crystal 3 from which the crystal bar I of Fig. 1 is grown may be any suitable seed crystal. The seed crystal 3 illustrated in Fig. 1 is a Z-cut crystal plate 3 having its four naturally grown edge faces coextensive with the four prism faces 5 of the crystal bar I, in which case the two cone sections 4 as shown in outline by broken lines in Fig. 1 may represent flawed cone sections in the crystal bar I which have been formed during the beginning of the growth of the crystal bar I from the Z-cut seed crystal plate 3. Alternatively, the sections 3 and 4 taken together may represent a naturally grown capped Z-cut seed crystal 3 and 4, from which the crystal bar I has been grown directly. The sections of the crystal bar I disposed beyond the ends of the sections 4 may represent clear good'quality crystal material from which piezoelectric plates may be cut for use as circuit elements in electrical systems generally.

The crystal plate III or I, as shown in Figs. 1 and 2, illustrates a diagonal seed plate in accordance with this invention, which has been cut from the mother crystal bar I. The orientation of the diagonal seed plate III or II) may correspond to the orientation of any of the natural cap or pyramidal faces I which follow the IIII planes of the crystal bar I. This results in an orientation for the diagonal seed plate I0 or ID wherein one set of the opposite edges of the faces I2 and I4 of the seed plate I0 extends in an a-axis direction, and the two major plane faces I4 of the diagonal seed plate III are parallel or nearly parallel to the plane of a can face I and in the case of ammonium dihydrogen phosphate, are inclined at an angle of 0=about 44 degrees and 47 minutes with respect to the optic axis Z. The diagonal seed plate I0 may be cut to any convenient thickness dimension such as down to 1 inch for example.

As illustrated in Fig. 1, the four small edge faces I2 and I2 of the diagonal seed plate In or In may be comprised of the four naturally grown prism faces 5 of the crystal'bar I, the two major plane faces I4 of the seed plate III or III being cut faces. While a series of such diagonal seed plates II) or III of the same orientation may be cut from other portions of the crystal bar I, the seed plate III, as shown in Fig. 1, is cut from the original seed area 3 and 4 of the crystal bar I. This region 3 and 4 ordinarily includes waste piezoelectric material, but in accordance with this invention, a useful seed plate Ill may be obtained from the region 3 and 4 of the crystal bar I. Accordin ly. the diagonal seed plate I0 cut from the flawed region 4 as shown in Fig. 1, may contain some flawed crystalline material 4 in the central regions of the seed plate I 0 away from the peripheral edges I2 and I2 thereof, and still be used in growing a good crystal bar II therefrom, as illustrated in Fig. 3..

Fig. 3 is a side view of an ammonium dihydrogen phosphate crystal bar II as grown from a diagonal seed plate III or III of the type and 4 orientation shown in Figs. 1 and 2. The crys tal bar I I of Fig. 3 may be grown from the diagonal seed plate II) or I0 in a nutrient solution in a known manner, the Z-axis length of the crystal bar I I being dependent upon the time of growth in the nutrient solution. and the aaxis cross-section'of the crystal bar II being determined by the projected a-axis dimensions of the seed plate III or III from which the crystal bar II is grown. Due to the orientation of the seed plate III or III from which the crystal bar II is grown, it will be noted that the cap or pyramidal faces I thereof may be of different resultant lengths but of the same angular orientation with repsect to the crystallographic axes Z and a'.

For the purpose of growing the seed plate III or I 0' into the crystal bar II of Fig. 3, the seed plate I I) or III may be mounted in suitable crystal growing apparatus in any suitable manner, such as for example by one or more supporting stainless steel wires 8 having ends extending into small holes 9 that may be drilled in the seed plate I3 at the peripheral region labeled 9 in Fig. 2. If these holes 9 are placed near the corners of the seed plate III and are shallow, the plate III can be suitably mounted to a plastic support as shown in Figs. 4 to 6 with the stainless steel wires I and so that the generally most useful 45-degree Z-cut piezoelectric plates can be cut therefrom without crystal wastage in or near the regions where the crystal seed I II was mounted.

In commercial crystal bar growing, it is often desirable that the crystal bar II of Fig. 3 be grown with predetermined approximate a-axis dimensions, and this requirement involves the dimensions of the diagonal seed plate III, which is oriented with its crystallographic axes Z and,

a coinciding with those of the grown crystal bar II. The seed plate I0 so oriented with its crystallographic axes coinciding with those of the crystal bar II may be a suitable seed for growing the crystal bar II, provided the peripheral edges of the seed plate I0 touch or coincide with each of the expected four prism faces 5 in at least one point. It is quite unimportant if the central portions of the seed plate I0 are imperfect since a suitable crystal bar II may be produced therefrom if the peripheral edges I2 and I2 of the seed plate I 0 are of clear material of uniform orientation and at least 1; inch thick. Also, seed plates I I! having small purely mechanical defects such as broken or cut corners and small chips out of the edges I2 and I2 will heal over in the growing process. It will be understood that diagonal seed plates III which are cut from the center regions 3 and 4 of the crystal bar I of Fig. 1 may have flawed crystal material on their major faces I4, but since these surfaces are surrounded by good solid crystal, such a diagonal seed plate III will heal over quickly when grown and give a good crystal bar II, as illustrated in Fig- 3.

Alternatively, as shown in Fig. 3, a crystal bar II may be grown from an essentially unflawed diagonal type seed plate, such as III in Fig. 1, that shows such perfect joining of the crystal bar II onto the major faces I4 of the diagonal seed plate III that the whole crystal bar II, even the portions containing the original seed material, can thereafter be used for cutting therefrom unflawed usable piezoelectric plates. While the major faces I4 of the diagonal seed plate I0 are cut parallel to and closely approximate the orientation of the naturally grown pyramidal cap faces 5 I of the crystal bar I of Fig. i,'they may depart slightly from that ltl plane by at least one-half degree for crystals ll whose a-axis dimensions can be economically used for making piezoelectric plates therefrom for use as circuit elements in piezoelectric systems. Crystal bars ll grown from diagonal seed plates I which have no flaws are practically free from veils and other crystal flaws running through the interior of the crystal bar ll. These and other improved results give the diagonal seed plate It an advantage over other types of seeds that are used for growing crystal bars.

Seed plates which are cut with their major surfaces approximating to the orientations of naturally growing crystal faces, of the type of out ID, are useful not only as seed crystals in growing ammonium dihydrogen phosphate crystals II but also are useful for growing other kinds of crystals from a suitable nutrient solution. Depending on the growth habit and form of the particular crystal being grown, the diagonal plate type of seed ill may be used for growing crystals other than ammonium dihydrogen phosphate crystals and similar tetragonal crystals such as potassium dihydrogen phosphate, ammonium dihydrogen arsenate and potassium dihydrogen arsenate. Analogous seed plates can also be cut from crystals of other classes, depending upon the crystallizing habit of the crystal. In general, where the seed crystal plate, such as the seed plate It or it, can be cut with its two major plane faces disposed parallel to and in the same crystallographic orientation as that of a surface which is natural to the growing habit of the crystal material and on which crystal growth will take place, it may be utilized for growing a crystal therefrom in connection with other classes of crystal material than those particularly mentioned in this specification.

Figs. 4 to 6 are views: illustrating a form of crystal support which may be utilized for mounting two seed crystal plates III or l0 and for growing such seed plates, in a suitable nutrient solution, into crystal bars I I of the type illustrated in Fig. 3. In the particular mounting arrangement shown in Figs. 4 to 6, the two seed plates It or II, which may be of different thickness dimensions as illustrated by the two crystal plates It in Fig. 4, are each carried by four wires 8, such as stainless steel or other suitable wires 8. The ends of each of the four supporting wires 8 may extend horizontall into four corresponding small and shallow holes 9 which may be drilled into the two opposite edge faces I2 of each seed plate It near the four corners thereof. The holes 9 being small, shallow and disposed near to the corners of the seed plate Ill do not extend far enough into the plate Ill to interfere with and cause damage or waste in the crystal material that comprises the interior regions of the plate It and bar ll grown therefrom.

As particularly illustrated in Figs. and 6, the

' ends of each of the supporting wires I may be provided with a short sleeve l5 composed of plastic or other suitable resilient material which is inserted in the corresponding hole 9 of the seed plate It, the sleeve I5 being compressed between the wall of the hole 9 and the outer surface of the wire'8. The sleeves it accordingly provide '1 tight and resilient fit for firmly mounting the disposed shaft 3 l.

6 seed plate It on the supportin wires 8 without danger of cracking the seed plate ll.

As illustrated in Figs. 4 to 6. the supporting wires 8 may be carried by U-shaped supports ii, the wires I extending horizontally through corresponding openings ll inthe prongs ll of the U- shaped supports 2|, which may be constructed from plastic or other suitable material. The two U-shaped supports Il may each be secured at an inclined position by means of suitable bolts 23 and pins 2| to the opposite ends of a horizontally disposed radial arm 21, which may be constructed ofplastic or other suitable material. The radial arm 21 may be secured at its center by a bolt 20 to a slotted portion in the vertically Other horizontally disposed radial arms similar to the radial arm 21 maybe provided at suitable intervals along the entire vertical length of the shaft SI for the purpose of mounting additional seed plates It to the shaft 3| in the manner that the two seed plates II, as shown in Fig. 4, are mounted and carried by the vertical shaft ll.

Suitable means, as disclosed for example in the A. N. Holden application hereinbefore mentioned, may be provided for supporting and rotating the vertical shaft II in a reciprocating rotary motion about its vertical axis, and thereby moving the seed plates III of Fig. 4 in contact with the nutrient solution for the purpose of growing each of the seed plates it into crystal bars H of the type shown in Fig. 3.

As shown in Fig. 3, the growth of the crystal bar ll consisting in particular of crystalline ammonium dihydrogen phosphate takes place mainly on the two major faces I! of the seed plate it and is in the general direction of the optic axis Z which in the example illustrated, is disposed at an acute angle 0 with respect to the major faces ll of the seed plate It. Accordingly, when it is desired that the crystal bar H be grown in the vertical direction. the major faces ll of the seed plate It may be mounted at the same angle 0 with respect to-the vertical direction as illustrated in Fig. 4, so that the growth on the major faces ll of the seed plates II will take place in the vertical direction. For this purpose, the major faces ll 01 the seed plates III and the planes of .the U-shaped -crystal supports 2| have been inclined at a suitable angle with respect to the vertical shaft 3|: as illustrated in Fig. 4.

While the mounting of the seed plates It has been illustrated in Fig. 4 for growing the crystal bars H in the vertical direction, it will be understood that the seed plates it may be mounted for growing the bars II in any other direction by a suitable corresponding position for the mountin of the seed plates it. and while a particular means.

has been disclosed for mounting and growing the crystal seed plates It, it will be understood that any suitable crystallizer and mounting means may-be utilized for growing the crystal bars -H from the seed plates Ii.

Although this invention has been described and illustrated in relation to specific arrangements, it.

grown cap face of said grown crystal, and said face of said seed crystal having a, plurality of peripheral edges corresponding in number with and being substantially aligned with the corresponding grown prism faces of said crystal body.

2. A piezoelectric crystal body grown from a seed crystal cut from another crystal, said seed crystal having a, face upon which said crystal body is grown, said face of said seed crystal being a face extending substantially parallel to a grown cap face of said grown crystal, and said face of said seed crystal having a plurality of peripheral edges corresponding in number with and being substantially aligned with the corresponding grown prism faces of said crystal body, said grown crystal body being of tetragonal form having four of said prism faces, aid grown cap face of said crystal body and said cut face of said seed crystal being substantially plane parallel surfaces.

3. A piezoelectric crystal body grown from a seed crystal cut from another crystal, said seed crystal having a face upon which said crystal body is grown, said face of said seed crystal being a face extending substantially parallel to a grown cap face of said grown crystal, and said face of said seed crystal having a plurality of peripheral edges corresponding in number with and being substantially aligned with the corresponding grown prism faces of said crystal body, said grown crystal body being of tetragonal form having four of said prism faces, said grown cap face of said crystal body and said cut face of said seed crystal being substantially plane parallel surfaces, said grown crystal body and said flawed regions adjacent said major faces of said seed plate.

7. A piezoelectric crystal grown from a seed crystal plate, said seed plate having two major faces cut parallel .to, or in the same crystallographic orientation as, that of a surface which is natural to the growing habit of the crystal and on which crystal growth will take place, and said seed plate being mounted for growing by supports seed crystal comprising ammonium dihydrogen phosphate.

4. A piezoelectric crystal body grown from a seed crystal plate cut from another crystal, said seed crystal plate having a pair of substantially plane parallel major faces upon which said crystal body is grown, said major faces of said seed crystal plate being faces extending substantially parallel to a grown cap face of said grown crystal body, each of said major faces being of similar shape and having a plurality of peripheral edges corresponding in number with and being in substantial alignment with the corresponding grown prism faces of said grown crystal body.

5. A piezoelectric crystal body grown from a seed crystal plate cut from anoth r crystal, said seed crystal plate having a pair of substantially plane parallel major faces upon which said crystal body is grown, said major faces of said seed crystal plate being faces extending substantially parallel to a grown cap face of said grown crystal body, each of said major faces being of similar shape and having a plurality of peripheral edgescorresponding in number with and being in substantial alignment with the corresponding grown prism faces of said grown crystal body, said grown crystal body and said seed crystal plate comprising ammonium dihydrogen phosphate.

6. An artificially grown piezoelectric crystal bar comprising as a part thereof a diagonal seed crystal plate, the prism faces of said crystal bar being grown coaligned with the corresponding outermost peripheral edges of said crystal seed plate, and the two major faces of said crystal seed plate extending substantially to said prism faces being faces cut substantially parallel to a pyramidal cap face, or 101 plane, of said crystal bar, said crystal bar comprising uniformly oriented crystalline material that is substantially free from extending into shallow holes drilled into a selected region of said seed crystal plate, said region corresponding to a region where said holes will not damage those portions of said grown crystal bar which are desired for cutting into piezoelectric crystal elements, said region for said holes being in the periphery adjacent the comers of said seed crystal plate, and said supports being wires inserted in said holes.

8. A piezoelectric crystal bar grown from a seed crystal plate cut from another crystal, said seed crystal plate having two major faces, said major faces being faces cut parallel to a surface natural to the growing habit of the crystal and on which crystal growth will take place, said surface and said cut major faces being substantially parallel to a grown cap face of said crystal bar, and means for mounting said seed crystal plate comprising supports extending into holes in said seed crystal plate.

9. A diagonal type seed crystal plate cut from a piezoelectric mother crystal and adapted for growing another piezoelectric crystal in a nutrient solution, said seed plate having a pair of major faces and a plurality of peripheral edge faces extending between said pair of major faces, said major faces being substantially parallel with respect to a 101 plane of said mother crystal, said peripheral edge faces extending in the direction of the Z-axis and comprising the naturally grown prism faces of said mother crystal, said seed plate comprising a part of the initial seed region of said mot-her crystal.

10. A diagonal type seed crystal plate cut from a piezoelectric mother crystal and adapted for growing another piezoelectric crystal in a nutrient solution, said seed plate having a pair of major faces and a plurality of peripheral edge faces extending between said pair of major faces, said major faces being substantially parallel with respect to a 101 plane of said mother crystal, said peripheral edge faces extending in the direction of the Z-axis and comprising faces cut substantially parallel to the naturally grown prism faces of said mother crystal, said seed plate comprising a part of the initial seed region of said mother crystal.

11. A diagonal type seed crystal plate cut from a mother crystal and adapted for growing another crystal in a nutrient solution, said seed plate having a pair of major faces and a plurality of peripheral edge faces extending between said pair of major faces, said major faces being substantially parallel with respect to a 101 plane of said mother crystal, said peripheral edge faces extending in the direction of the Z-axis and comprising the naturally grown prism faces of said mother crystal, said seed plate comprising a part of the initial seed region of said mother crystal, and comprising one of the crystalline substances ammonium dihydrogen phosphate, potassium dihydrogen phosphate, ammonium dihydrogen arsenate and potassium dihydrogen arsenate.

12. A diagonal type seed crystal plate cut from a mother crystal and adapted for growing another crystal in a nutrient solution, said seed plate having a pair of major faces and a plurality Y of peripheral edge faces extending between said pair of major faces, said major faces being substantially parallel with respect to a 101 plane of said mother crystal, said peripheral edge faces extending in the direction of the Z-axis and comprising faces cut substantially parallel to the naturally grown prism faces of said mother crystal, said seed plate comprising a part of the'initial seed region of said mother crystal, and comprising one' of the crystalline substances ammonium dihydrogen phosphate, potassium dihydrogen phosphate, ammonium dihydrogen arsenate and potassium dihydrogen arsenate.

13. A seed crystal plate cut from a tetragonal mother crystal, said seed plate having its four edge faces substantially parallel to the Z-axis and its two major faces substantially parallel to a naturally grown pyramidal cap face of said mother crystal, said seed plate comprising a part of the initial seed region of said mother crystal.

14. A seed crystal plate cut from a grown tetragonal mother crystal, said seed plate having its four edge faces substantially parallel to the Z- axis and its two major faces substantially parallel to a grown pyramidal cap face of said mother crystal, said seed plate comprising a part of the initial seed region or said mother crystal and said seed plate comprising crystalline ammonium dihydrogen phosphate.

15. A crystalline seed plate having two major faces adapted for growing a tetragonal crystal bar from at least one of said two major faces in the direction of the Z-azds, said seed plate having at least a part of its peripheral edges lying in each the four prism faces of said crystal bar to be grown therefrom, said seed plate having its said two major faces disposed substantially parallel to a grown pyramidal cap face of the mother crystal from which it is out. said seed plate comprising at least a part of the initial seed region of said mother crystal.

16. A crystalline seed plate having two major faces adapted for growing a tetragonal, crystal bar from at least one of said two major faces in the direction of the Z-axis, said seed plate having at least a part of its peripheral edge lying in each of the four prism races of said crystal bar to be grown therefrom, said seed plate having its said two major faces disposed substantially parallel to a grown pyramidal cap face of the mother crystal from which it is cut, said seed plate comprising at least a part of the initial seed region of said mother crystal, said seed plate comprising crystalline ammonium dihydrogen phosphate.

17. A crystalline ammonium dihydrogen phosphate seed crystal plate cut from a mother crystal, said seed plate having its major faces substantially parallel to the plane of one of the grown pyramidal cap faces or a 101 plane or said mother crystal, said seed plate comprising at least a part of the initial seed region of said mother crystal.

CARL J. CHRISTENSEN.

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Mendelssohn, Nature, 144; 595 (1939).

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